Sphalerite is a mineral which is the chief ore of zinc. It consists largely of zinc sulphide in crystalline form and variable amounts of iron. When iron content is high it forms an opaque black variety called marmatite.

Sphalerite is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite and fluorite. Miners refer to sphalerite as zinc blende and black-jack.

Its color is usually yellow, brown, or gray to gray-black. It may be shiny or dull. Its luster varies from resinous to sub-metallic for high iron varieties. It has a yellow or light brown streak. It measures 3.9 to 4.1 in Moh’s scale of mineral hardness.

Ruby Sphalerite has a red iridescence within the gray-black crystals. The pale yellow and red varieties have very little iron and are translucent. The darker and more opaque varieties contain more iron. Some specimens are fluorescent in UV rays.

An almost pure Zinc Sulfide variety known as cleiophane, is highly fluorescent under long wave ultraviolet light .

Crystals of suitable size and transparency are fashioned into gemstones. Their brilliant cut displays sphalerite’s high dispersion – over three times that of diamond. Freshly cut gems have an adamantine luster.

Owing to the softness and fragility the gems become collector’s items and museum pieces. Some have been set into pendants. Gem-quality material is usually a yellowish to honey brown, red to orange, or green.